Peening is a surface treatment or process that creates residual compressive stresses in component surfaces. Conventional techniques include (but are not limited to) shot peening, pneumatic peening, and laser surface peening. Peening is directed at imparting stress to a surface (e.g., metal or alloy) to pre-condition the surface against wear and stresses that are encountered throughout the component's life span.
For example, laser surface peening has been used to increase the resistance of aircraft gas turbine engine compressor and fan blades to damage and increase their useful life (e.g., via preventing or reducing high cycle fatigue). Laser surface peening, as with other peening processes or treatments, creates residual compressive stresses in component surfaces.
Laser surface peening is therefore used to provide compressive stress to the surface of a component (e.g., aircraft engine fan blade) to prevent the formation of fatigue cracks in the surface of the component and to reduce the propagation of such fatigue cracks once formed. Laser surface peening drives a high-energy (amplitude) shock wave into a component surface using a pulsed laser. The laser heats an overlay material (e.g., underlying opaque material and upper transparent material) such that the opaque overlay material absorbs the energy from the laser pulse and produces a shock wave, directed downward into the part surface (assisted, e.g., via the upper transparent layer of the overlay material). Laser surface peening therefore provides a mechanical stress (in turn brought about by the shock wave rather than a thermal treatment from heat generated by the laser at the surface).
Laser surface peening has been employed to impart residual compressive stresses of up to about 1 mm in depth. Laser surface peening has been particularly effective in aircraft engine titanium alloy fan and compressor blade applications and other small-scale (thin component) applications.